1. Field of the Invention
The present invention generally relates to a semiconductor device capable of coping with overheating and an over-current by providing a temperature detector and a current detector; and especially relates to a semiconductor device that includes a power circuit capable of sending out an alarm signal to an external circuit before abnormalities occur in the power circuit, and an electronic apparatus, such as a cellular phone, incorporating the semiconductor device.
2. Description of the Related Art
Background Technique
A semiconductor device that includes a power circuit for supplying a current to a load uses a power transistor for controlling an output voltage and a load current. Such a semiconductor device generates heat in connection with a large current flowing through the power transistor. In order to reduce the heat generated, conventionally, a current limitation circuit is widely used.
Here, the temperature of the semiconductor device is dependent on consumed electric power and the ambient temperature. Accordingly, if, for example, the ambient temperature is low, and/or if an electric voltage applied to the power transistor is low, a current greater than dictated by the current limitation circuit may be allowed to flow. On the contrary, there can be a case wherein the temperature of the semiconductor device exceeds a maximum rating before the current limitation circuit triggers. That is, protection of the semiconductor device cannot be adequately provided only by the current limitation circuit.
For this reason, conventionally, an overheat-protection circuit for limiting the current of the power transistor is additionally used, wherein a temperature sensing element is arranged in the vicinity of the power transistor for determining whether the temperature of the vicinity of the power transistor reaches a predetermined temperature.
Further, where the semiconductor device includes two or more power circuits for supplying power to different loads of a system, one of the power circuits may stop power supply due to an over-current and overheating, which causes a breakdown of the system.
In an attempt to cope with the situation as described above, Patent Reference 1 discloses a technique of identifying a power circuit causing unusual generation of heat, and selectively carrying out protection control.
According to the technique, a semiconductor chip including two or more power circuits and a microprocessor constitute a hybrid IC; a temperature detector is built into the semiconductor chip and is densely thermally coupled with a power transistor of a power circuit; if a temperature detected by the temperature detector exceeds a predetermined temperature threshold, the microprocessor turns off a power transistor of the power circuit, the flowing current of which exceeds a predetermined current value.
[Patent reference 1] JPA 2002-232280